拨号对等配置：7位拨号，10位拨号，和重叠拨号计划

在下一个例子中配置用于操纵的7位本地拨号（具有9个接入码前缀），以本地PRI资源（0/0/0：23）：拨号等语音201个盆目的地图案9 [2-9]…… Port 0/0/0:23 If you’re deploying a solution in major metropolitan area, the PSTN provider will probably not allow 7 digit dialing, so you will not have to include this pattern in your dial plan. 7 digit dialing is still an option in rural areas (Dutchess County, NY as an example) and smaller metropolitan areas like Albuquerque, New Mexico. Since POTS dial-peer forward wildcards and the destination-pattern has 7 wildcards, no digit manipulation is required. The forward-digits 7 command in the dial-peer would allow an easier understanding of the dial plan if the customer or IT support staff does not want to be troubled remembering default dial-peer digit consumption rules. The dot (.) is a wildcard that matches any single digit (zero through nine) in a very similar way to how CUCM used the X character in dial plan configurations. The leading digit of the three digit exchange (NXX) in the 7 digit pattern will not match on a zero or one because the zero and one is not allowed as a leading digit in the current NANP. Zero on the PSTN is normally reserved for the operator, while a 1 is reserved as the long distance code. We will talk more about this as this blog conversation progresses. The next example configuration is used to route 10 digit phone calls to any area code: Dial-peer voice 202 pots Destination-pattern 9[2-9]..[2-9]…… Port 0/0/0:23 The leading digit of both the three digit area codes (NPA) and three digit exchange (NXX) do not match on a zero or one. The combination of local 7-digit dialing and 10-digit dialing in a gateway creates an overlapping dial plan condition shown below: [2-9]…… (7-digit dialing) [2-9]..[2-9]…… (10-digit dialing) Since this discussion revolves around the overlapping nature of 7 and 10 digit dialing, the example is ignoring the access code of 9. If a user dials a 7 digit number (e.g. 867-5309), the dialed digits match both the 7-digit and 10-digit destination-patterns used in two different dial-peers (tag 201 and tag 202 respectively). Cisco Unified Communications Manager (CUCM) would wait for the T.302 inter-digit timeout (15 seconds by default) to expire and then route the 7-digit call, but Cisco IOS does not have the same level of understanding for overlapping dial plans. The H.323 or SIP controlled Cisco IOS gateway will route the 7-digit call immediately because of the 7-digit pattern match on dial-peer 201 (created in the last blog entry). If a 10-digit number of (212) 867-5309 was dialed, the 7-digit pattern would match and the first 7 digits of the call 212-8675 would be attempted. The easy fix to the previous challenge in major metropolitan areas is to remove 7 digit dialing options from the gateway. There’s normally not a requirement to support 7 digit dialing in the enterprise if the local exchange carrier (LEC) will not route 7 digit phone calls. Unfortunately, this is not an option in areas that need to support 7 and 10 digit dialing. The Cisco IOS gateway uses longest match routing which is very similar to the closest match routing that CUCM uses when analyzing dialed digits against the configured dial plan. If the following two destination-patterns were used for 7 and 10 digit dialing (respectively), the 10 digit dialing would be fixed: 9T 9[2-9]..[2-9]…… The “T” character in destination-patterns matches on one or more digits. The T character used in Cisco IOS is very similar to the exclamation point “!” used in CUCM route patterns. It is not good design to use the 9T in only one dial-peer to represent the entire PSTN dial plan because every phone call matching the destination pattern will have to wait for the inter-digit timeout (10 seconds in Cisco IOS) to expire before routing the call. The example above only has this issue when dialing a 7-digit pattern. The inter-digit timeout is commonly changed to 5 seconds as documented in various Cisco best practice documents. In the next blog, we will discuss 11-digit long distance dialing in Cisco IOS based H.323 and SIP gateways.